Hornfels is a metamorphic rock formed by the contact between mudstone / shale, or other clay-rich rock, and a hot igneous body, and represents a heat-altered equivalent of the original rock. This process is termed contact metamorphism.

What is gneiss used for?

Metamorphic Gneiss has many uses as a building material such as flooring, ornamental stones, gravestones, facing stones on buildings and work surfaces.

Where are hornfels made?

Hornfels most commonly form in the aureole of granitic intrusions in the upper or middle crust. Hornfels formed from contact metamorphism by volcanic activity very close to the surface can produce unusual and distinctive minerals.